A number of mechanical grippers have been developed in the art which address the problem of grasping objects. Typically, these grippers are used in conjunction with some form of robot arm to which they are attached and, also typically, grasping/releasing motion is achieved by a pressurized operator mechanism which includes a cylinder and a piston, with the piston mechanically coupled to fingers or other means which grasp the object. Fluid pressure applied to one side of the piston causes the fingers to grasp the object, while fluid pressure applied to the other side of the piston causes the fingers to release the object. Such grippers are typified by the devices described in U.S. Pat. Nos. 4,492,400 and 4,540,212 and in copending U.S. application Ser. No. 852,614, assigned to the assignee of the present invention. In each of the grippers theredescribed, as well as in other known grippers of like type, when the piston is actuated to release the object, it moves to the maximum extent in the direction causing the release, thus causing the fingers to travel to their maximum open position, whether or not this extent of travel is necessary to release the object. In some cases, the maximum travel results in objectionable interference with other objects.
An example of such an objectionable interference is in the robotic placing of components on printed circuit boards, where the dense arrangement of components already inserted on a board complicates the inserting of additional components when the robotic gripper employed opens to its maximum extent each time a component is placed. The present invention minimizes this complication by limiting the extent of travel of the gripper upon release of an object, as hereinafter described.